The present invention generally relates to the electrical interconnection devices in general, and more particularly to contacts that are at the electrical interface between an integrated circuit package and a substrate or between an electrical connector and the same.
High density integrated circuit (IC) packages that house LSI/VLSI type semiconductor devices are well known. Input/output pins for such IC packages are often arranged in such a dense pattern (sometimes more than two hundred closely spaced contacts) that direct soldering of the IC package to a substrate, such as a printed wiring or circuit board (PCB) creates several significant problems related to inspection and correction of any resulting soldering faults.
Land grid array (LGA) connectors are known for interconnecting IC packages to PCB""s. LGA""s typically do not require soldering procedures during engagement with the PCB. Referring to FIG. 1, prior art LGA assemblies are used to interconnect an IC package 7 having a plurality of flat contact pads 12 formed on a bottom surface, to contact pads 16 arranged in a regular pattern on a surface of PCB 19. Current technology permits conductive pads 12 and conductive pads 16 to be disposed at center-to-center spacings (as indicated by dimension xe2x80x9caxe2x80x9d in FIG. 1) of approximately one half to one millimeter, with further miniaturization possible and inevitable.
Prior art LGA assemblies are known which include an insulative housing and a plurality of resilient conductive contacts received in passageways formed in the housing. The resilient conductive contacts typically have exposed portions at the upper and lower surfaces of the insulative housing for engaging flat contact pads 12,16. When IC package 7 is accurately positioned in overlying aligned engagement with PCB 19, such that conductive pads 12 engage conductive pads 16, a normal force is applied to the exposed portions of each resilient conductive contact to electrically and mechanically engage the respective contact pads.
The resilient conductive contacts associated with prior art LGA""s have had a variety of shapes. A commonly used form of resilient conductive contact includes two free ends connected by a curved portion which provides for the storage of elastic energy during engagement with the IC package and PCB. Prior art resilient conductive contacts are usually a single metal structure in the form of a spring to provide the required elastic response during service while also serving as a conductive element for electrical connection. Typically, a combination of barrier metal and noble metal platings is applied to the surface of the spring for corrosion prevention and for electrical contact enhancement. It is often the case that these platings are not of sufficient thickness for electrical conduction along the surface of the spring. Examples of such prior art resilient conductive contacts may be found in U.S. Pat. Nos.: 2,153,177; 3,317,885; 3,513,434; 3,795,884; 4,029,375; 4,810,213; 4,820,376; 4,838,815; 4,922,376; 5,030,109; 5,061,191; 5,232,372; and 5,473,510. The foregoing patents are hereby incorporated herein by reference.
One such problem in the art exists in that a good material for the construction of a spring, such as a high strength steel, is not a very good electrical conductor. On the other hand, a good electrical conductor, such as a copper alloy or precious metal, is often not a good spring material. There is a need for a more simplified resilient conductive contact which incorporates the seemingly opposing requirements of good spring properties and high conductivity. Therefore, an improved electrical contact for use in an LGA socket or electrical connector is needed which can overcome the drawbacks of conventional electrical contacts.
The present invention provides an electrical contact comprising a first member having spring properties and a second member wrapped around at least a portion of the first member wherein the second member has a greater electrical conductivity than the first member. In one embodiment, one or more conductors are wrapped around at least a portion of a spring to improve current carrying capability. In another embodiment, the spring is formed into a coil or helix with a wire wrapped around at least a portion of the helical spring. In one form of this embodiment, the spring has a plurality of turns and the wire is wrapped around at least two of the turns. In another form of this embodiment, the spring has a plurality of turns and the wire is wrapped around all of the turns. In a further alternative embodiment, multiple springs are enmeshed together to provide enhanced mechanical and electrical performance.
Thus the present invention provides, in general, an electrical contact having means for storing elastic energy and means for conducting electricity that are wrapped around at least a portion of the means for storing elastic energy. The means for conducting electricity advantageously has a greater electrical conductivity than the means for storing elastic energy.
In yet another embodiment of the invention, an interposer connector is provided having a frame including a top surface and a bottom surface and a plurality of apertures arranged in a pattern and opening onto the top and bottom surfaces of the frame. A plurality of springs are provided with each spring having a conductor wrapped around at least a portion of the spring where the conductor has a greater electrical conductivity than the spring. One of the springs is positioned within each of the apertures so that at least a portion of each of the conductors is exposed above the top and bottom surfaces of the frame. An electrical connector is also provided incorporating an electrical contact having spring means for storing elastic energy and means for conducting electricity that are wrapped around at least a portion of the spring means.